management icp

7/30/2019 Management ICP

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19 MANAGEMENT OFINTRACRANIAL PRESSUREAND CEREBRAL PERFUSION

Peter Reilly

19.1 Introduction

The treatment of traumatic brain injury is based on theconceptual distinction between primary and second-ary injury. Primary injury comprises the immediateeffects of impact. Secondary injury is due to factorsother than the direct impact and may begin almostimmediately or some time later. The distinction is ofcourse, not so sharp. It is increasingly clear that theimpact initiates a series of events, including anevolving axonal injury and release of mediator sub-stances, which cause injury over minutes to hoursafter impact, suggesting that it may become possibleto intervene therapeutically in the evolution of theseprocesses initiated by the primary injury.

Secondary injury, on the other hand, may begin at orvery close to the impact. Asphyxia or massive bloodloss may cause overwhelming ischemichypoxic sec-ondary damage, irrespective of the severity of the

primary injury.However the model of primary and secondaryinjury has clinical value and this chapter will concen-trate on the two of the main end points in managingthe secondary effects of injury, cerebral perfusionpressure (CPP) and intracranial pressure (ICP).

The major cause of raised ICP, apart from hemato-mas, is brain swelling. The factors responsible for

post-traumatic brain swelling are not clear. There isconvincing evidence for both cytotoxic and ischemichypoxic influences, and specific means of combatingthem are now emerging from the laboratory intoclinical trial. However, until brain swelling can be

prevented the primary goals in preventing secondary

brain injury will be to provide adequate cerebralperfusion and oxygenation and to prevent brain shift(herniation).

Ideally, treatment should be based on direct knowl-edge of regional CBF, metabolism and function.Although this may soon be possible, at present ICP

and CPP, which can be measured easily and con-tinuously, provide the best indirect measurements oftissue perfusion. ICP and CPP are however, globalmeasurements and this has implications in definingtreatment goals for a heterogeneous injury. This will

be discussed later. Indirect indices of CBF and metabo-lism, such as jugular venous oxygen saturation (PjvO2),transcutaneous Doppler (TCD; Chapter 14), electricalfunction (Chapter 13) and near-infrared spectroscopy(Chapter 11) may assist in defining adequate cerebralperfusion and oxygen delivery and in selecting themost appropriate treatment.

19.2 Intracranial pressure

Some aspects of ICP pathology relevant to the man-agement of head injury will be reviewed briefly. (Thissubject is covered in greater detail in Chapter 6.)

Our understanding of the relationship between

intracranial volume and pressure has its origin in theappreciation of Monro (1783) and Kellie (1824) thatcranial volume remains constant after sutural fusionand that the intracranial contents are incompressible.Burrows (1846) subsequently made the importantadditional observation that, while total volumeremains constant, CSF volume could interchange withblood volume. Hence provided that a change involume in one compartment is balanced by near-equalchange in another, ICP will remain constant.

The major intracranial volumes are brain par-enchyma (12001600 ml), blood (100150ml) and CSF(100150 ml; Figure 19.1). These latter two constituteabout 20% of total intracranial volume and part of

each is capable of rapid extracranial displacement.Therefore they are of prime importance in the volumeequilibration of an expanding mass.

The extracellular fluid component of brain par-enchyma is also capable of change, both patho-logically and in response to treatment. Therefore

Head Injury. Edited by Peter Reilly and Ross Bullock. Published in 1997 by Chapman & Hall, London. ISBN 0 412 58540 5


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386 MANAGEMENT OF INTRACRANIAL PRESSURE AND CEREBRAL PERFUSION

manipulation of these volumes underlies the treat-ment of raised ICP after head injury.

Since the landmark study of Lundberg (1960) on theclinical value of ICP monitoring, many studies have

drawn attention to the importance of raised ICP aftersevere head injury.

In one major trauma center, ICP was found to beelevated (to greater than 10 mmHg) in 82% of patientswith severe head injury. Of those with raised ICP,one-third (16% of the entire series) developed uncon-trolled intracranial hypertension and died. Con-versely, in about 50% of those who died, raised ICPwas the major cause. In survivors, moderately raisedICP was a major cause of morbidity (Miller et al.,1977; 1981).

In the multicenter Traumatic Coma Data Bank(TCDB) study from the USA, ICP was found to be animportant independent variable, significantly related

to outcome (Marmarou et al., 1991). Although in somepatients intracranial hypertension may simply be asign of an overwhelming and irrecoverable braininjury, the evidence for actively treating raised ICPderives mainly from the observation that mortality islower in those patients in whom ICP can be controlled(Eisenberg et al., 1988).

19.2.1 INTRACRANIAL PRESSURE AND CEREBRAL

PERFUSION PRESSURE

The relationships between ICP, CPP and brain functionare complex. However certain points can be made.

It is doubtful whether raised ICP itself directlyalters neuronal function. Although it has beensuggested that the effects of raised ICP on cellularmetabolism and membrane integrity may not beentirely related to CPP (Chesnut and Marshall,1993), it seems likely that the absolute level of ICP isnot as important as its effect on CPP and itsrelationship to brain herniation.

Reduced CPP and brain herniation are principalmechanisms of secondary brain damage followingsevere head injury (Johnston, Johnston and Jennett,1970; Rosner and Daughton, 1990). In support ofthis, raised ICP, even over 60 mmHg, withoutdisplacement and with adequate CPP may produceno neurological deficit. This is seen quite dramat-

ically in benign intracranial hypertension. In the absence of herniation, ICP measured in one

brain region will reflect the pressure of the entirecranial cavity (Langfitt, Weinstein and Kassell,1964a, b). Even so, its effects on regional perfusionmay be heterogeneous. Perfusion in and aroundareas of injury may be reduced further by anincrease in regional tissue pressure creating regionalpressure gradients, by vessel distortion or byregional loss of autoregulation. ICP and thereforeglobal CPP may thus overestimate regionalperfusion.

The viscoelastic properties of the brain as measuredby compliance tests are altered by brain injury(Figure 19.2(a)) and by the standard methods oftreating raised ICP (Figure 19.2(b)). Mannitol com-pared with hyperventilation increases complianceat the same pressure level (Leech and Miller, 1974;Rowed et al., 1975).

19.2.2 INTRACRANIAL PRESSURE GRADIENTS

Interhemispheric pressure gradients are not observedin patients with diffuse injury but can occur in patientswith focal lesions and midline shift and may lastseveral hours (Sahuquillo et al., 1994). In this lattergroup, ICP might best be measured from the side ofthe focal lesion.

The relationship between ICP and cerebral hernia-tion is variable. Herniation is the result of a pressuregradient between anatomical compartments gener-ated by an expanding mass, but the speed of devel-opment depends on anatomical factors and determi-nes the functional significance of the herniation.Temporal lobe masses can only expand medially andposteriorly, being constrained anteriorly, laterally andinferiorly by bone. They will therefore result in moretentorial herniation at lower ICP than will occipitalor frontal masses. The lateral displacement of deep

brain structures may itself be an important basis forloss of consciousness through the shearing effect on

small perforating vessels to deep diencephalic struc-tures (Andrews et al., 1988; Ropper, 1986, 1989;Marshall et al., 1983). Herniation is a form of volumecompensation for high ICP and once herniation and

brain-stem compression have occurred, the inter-compartmental pressure gradients will disperse andICP may even be low for a short time (Johnston and

Jennett, 1973).

Figure 19.1 The major intracranial contents by volume.


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INTRACRANIAL PRESSURE 387

19.2.3 THE GENESIS OF RAISED INTRACRANIAL

PRESSURE

Marmarou, Shulman and LaMorgese (1975) devel-oped a theoretical model of ICP based on a constantproduction of CSF independent of pressure, circula-tion through a compliant storage space and absorptionvia pressure-dependent outflow pathways at thearachnoid villi. Dural sinus pressure was defined asthe exit pressure of the system. The steady staterelationship may be expressed as:

ICP = IfRo+ PD

whereIf = formation rate; Ro = outflow resistance; PD= dural sinus pressure.

In this model, steady state ICP is proportional to:

rate of CSF formation; resistance to CSF absorption; dural sinus pressure.

The factors leading to raised ICP can be considered asbeing of CSF or vascular origin.

The CSF component of ICP derives from the productof CSF formation and outflow resistance. Pathologicalevents that increase the CSF component are associatedwith an increase in brain water. This may take the formof ventricular dilatation or brain edema.

The vascular component of ICP under normalphysiological conditions is equivalent to dural sinuspressure. Pathological events that affect the vascularcomponent are associated with dilatation of thevascular bed and congestive or hyperemic brainswelling. The contribution of these two components toraised ICP can be determined by analysis of pressurevolume relationships. In head-injured patients, vas-cular factors are twice as common as non-vascularfactors and make the major contribution to raised ICP,probably from compression of compliant veins (Mar-marou et al., 1987). Hyperemic swelling is particularlycommon in children (Muizelaar et al., 1989)

(a)

(b)

Figure 19.2 The influence of viscoelastic changes on thevolume pressure curve. (a) Edema and hemorrhage reducecompliance, as well as take up volume. Hence pressurebegins to rise sooner and more steeply. (b) Mannitol reducesbrain volume and shifts the curve to the right. The brain ismore compliant, hence the initial curve is f latter. Hypocarbiareduces blood volume and also shifts the curve to the rightbut does not alter compliance (the slope of the curve).


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19.3 Cerebral perfusion pressure

Perfusion pressure across any vascular bed is themean systemic arterial pressure minus venous out-

flow pressure. Intracranial venous outflow pressure atthe dural sinuses (the pressure in the cerebral veinswithin the subarachnoid space) remains slightly

above and is linearly related to CSF pressure over awide range, so in practice cerebral perfusion pressure(CPP) = mean BP mean ICP (Rowan et al., 1972).

Normally, within a CPP range of 60160mmHg, CBFremains constant. However, in brain injury thisautoregulatory relationship may be altered by anumber of factors.

CPP is equivalent to the transmural pressure acrossthe cerebral vessel walls. CPP at the arteriolar level isthe stimulus for the autoregulatory response and, atthe capillary level, is the driving force for fluidexchange.

19.4 Intracranial volumes

19.4.1 CEREBRAL BLOOD VOLUME

Some 70% of cerebral blood volume (CBV) resides inthe capacitance vessels. As CPP falls, arteriolar dilata-tion occurs in an attempt to maintain constant CBF.CBV will vary with these autoregulatory adjustmentsin vessel diameter. Within the autoregulatory range, asCPP rises, arteriolar constriction leads to a fall in CBVand hence in ICP. Below the autoregulatory range,maximal vasodilatation has occurred but, if CPP fallsfurther, CBV will fall paradoxically as a result ofvasocollapse (Kontos et al., 1978)

Hence, although CBV and ICP are directly related,the relationship between CBF and CBV depends on thestatus of autoregulation and the level of CPP.

Hypoxia causes cerebral vasodilation at PaO2 levelsbelow 50 mmHg. The stimulus for vasodilatation isreduced oxygen delivery and therefore depends onHb, CBF and O2 saturation.

CO2 is also a cerebral vasodilator probably actingthrough H+ concentration in smooth muscle cells ofthe cerebral vessels (Gotoh, Meyer and Takagi, 1965).The relationship between PaCO2 and CBF is sigmoid(Harper and Glass, 1965). Within the range of3050 mmHg CBF bears a linear relation to PaCO2(Hayes and Tindall, 1969; Paul et al., 1972). The CO2response is very robust and is usually at least partly

preserved after severe head injury, even when pressureautoregulation is lost.

Indeed the absence or severe reduction of the CO2response has serious prognostic significance (Shalen,Messeter and Nordstrom, 1991; Cold, Jensen andMalmros, 1977; Enevoldsen and Jensen, 1978; Over-gaard and Tweed, 1974; Yoshihara, Bandoh and

Marmarou, 1995). It may also predict failure torespond to barbiturates (Nordstrom et al., 1988) sincethe ability of these drugs to reduce ICP dependsupon the capacity of the cerebral vessels to respond

by vasoconstriction to reduced metabolic demand.

19.4.2 CEREBROSPINAL FLUID VOLUME

Some 70% of CSF is produced by the choroid plexusand 30% enters the ventricles across the ependymafrom brain parenchyma as excess extracellular fluid(brain lymphatic fluid). CSF production involvesactive transport, particularly of Na+, and may bereduced by the carbonic anhydrase inhibitor acet-ozolamide (Rubin et al., 1966; Sahar and Tsipstein,1978), by frusemide (furosemide) and steroids (Satoet al., 1973). The rate of production is constant atabout 0.35 ml/min (20 ml/h or 500ml/d) giving afivefold turnover per day. Production is not influ-enced by ICP except at very high levels (Brgesen

and Gjerris, 1989).Total CSF volume in an adult is approximately

140ml, of which 30ml is spinal and 20ml in theventricles (Davson, Welch and Segal, 1987).

A total of 80% absorption occurs via the arachnoidgranulations, particularly those related to the duralsinuses, and at normal pressures is determined both

by the pressure gradient across the granulations andby active transport. The other 20% is absorbed viaspinal nerve root sheaths and the VirchowRobinperivascular spaces. Hence CSF absorption increaseswith ICP. It can be inhibited by obstruction in anypart of the CSF pathways or at the arachnoid villi.

19.4.3 BRAIN VOLUME

Brain volume contributes about 70% of intracranialvolume and is normally constant. Traumatic brainswelling may be due to an increase in one or moreof the three brain fluid compartments blood,intracellular or extracellular fluid and is the majorcause of raised ICP after head injury. (See Chapter 7for a detailed discussion of traumatic brain swell-ing.) Brain is the least displaceable of the intracranialvolumes. Displacement or herniation of brain is alimited and final form of accommodation of anintracranial mass.

19.5 Volumepressure relations

The initial, nearly horizontal part of the exponentialvolumepressure curve represents the phase whenintracranial (venous) blood and CSF can be readilydisplaced to accommodate an increase in another


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VOLUMEPRESSURE RELATIONS 389

volume or the addition of a new volume, without risein pressure. Further volume additions (V) causeincreasingly steep rises in ICP as the force needed todisplace compensating fluid volumes increases Therelative contribution of the two chief displaceablevolumes, blood and CSF, are represented in Figure19.3 (Rosner, 1993).

CSF can be displaced readily into the spinal sub-arachnoid space. A total of 70% of the CSF bufferingcapacity is contained in the intracranial compartmentand 30% in the spinal compartment, where duralexpansion can occur by compression of epidural veins(Marmarou, Shulman and LaMorgese, 1975). Blockageat the foramen magnum by tonsillar herniation pre-vents this compensatory displacement and acceleratesfurther rapid rises in ICP.

CBV within the venous (capacitance vessels) can bereadily and passively displaced to the extracranialvenous system. A smaller volume of blood is con-tained on the arterial side but the reactivity of thearterioles (autoregulation) has a major influence onCBV and hence on ICP as already outlined.

19.5.1 INTRACRANIAL PRESSURE WAVES

Lundberg (1960) first recognized the significance ofpressure waves occurring under conditions of reducedintracranial compliance. Of the three main waves hedescribed, A waves (Plateau) and the shorter durationB waves are of greatest clinical relevance. Rosner

(Rosner and Becker, 1984a) has attributed them to areduced CPP, which leads to a vasodilatory cascade.

Providing CPP is within the autoregulatory rangeand autoregulation is preserved, a fall in CPP willinduce vasodilatation, an increase in CBV and a

parallel increase in ICP. This will further reduce CPPand tend to perpetuate the circle.

The process may be terminated by a rise inBP (Cushing response) the increase in CPP willthen lead to vasoconstriction and a fall in CBV or by hyperventilation, which reduces ICP byvasoconstriction.

19.5.2 MEASURING INTRACRANIAL VOLUME

RESERVE

Theoretically, measurement of intracranial volumereserve would allow treatment of brain swelling

before ICP rises (Marmarou, 1986). However com-pliance measurements (the pressure rise associatedwith a given volume increase) have not gained a placein routine clinical practice and it is not known whethersuch a pre-emptive approach would make thetreatment of brain swelling more effective. However,compliance measurements have given some insightsinto the effects of head injury and various treatments.Following head injury, compliance increases, alteringthe shape of the volume pressure curve so that it risesmore steeply, and the breakpoint, the point at whichICP begins to rise, may be moved to the left, indicatinga reduced buffering capacity (Figure 19.2(a)).

Treatments used to reduce ICP may also affectcompliance. Hyperventilation moves the breakpointto the right, increasing the intracranial bufferingcapacity, but does not change its slope (Rowed et al.,1975). Yoshihara, Bandoh and Marmarou (1995)found that the PVI, and hence the slope of thevolumepressure curve did not change with moder-ate changes of PaCO2. Mannitol appears to shift the

breakpoint and also to change the slope of the curve,so having the additional advantage of rendering the

brain more compliant (Leech and Miller, 1974; Figure19.2(b)).

19.5.3 VISCOELASTIC PROPERTIES

As indicated by the changing slope of the volumepressure curve under different circumstances, the

viscoelastic properties of the brain, the skull and thedural sac affect the equilibrium relationship betweenICP and intracranial volume. If the brain is tight(high elastance, low compliance), a small volumeaddition will produce a marked rise in ICP. Hencepathological processes, such as brain edema, willaffect volumepressure relationships both by theincrease in volume of tissue water and by altering the

Figure 19.3 The contribution of CSF, venous and arterialblood volume displacement to the volume pressure curve.Pressure is defined here as the force necessary to displacecontents. The volume pressure curve is seen as the resultantof curves derived from the pressure necessary to displace

CSF, venous and arterial blood. (Source: reproduced fromRosner, 1993, with permission)


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viscoelastic properties of the brain The relationshipbetween CSF inflow and outflow and viscoelasticityare represented in Figure 19.4 (Miller, 1985).

19.5.4 IDENTIFYING THE CAUSES OF RAISED ICPAFTER HEAD INJURY

After mass lesions (e.g. hematomas ) have beenexcluded and extracerebral factors such as raisedintrathoracic pressure or hyperthermia have beenrectified, persistently raised ICP is likely to be due to

brain swelling.Brain swelling may be due to hyperemia (vascular

engorgement, mainly venous) or edema (an increase inbrain water content). Brain edema has been furtherclassified as cytotoxic, vasogenic or hydrostatic(Chapter 7).

Ways of identifying the vascular and non-vascularfactors contributing to raised ICP by a combination ofICP wave form analysis, cerebral electrical functionmonitoring and continuous monitoring of jugularvenous oxygen saturation have been suggested (Piper,Dearden and Miller, 1989; Dearden and Miller, 1989).

Jugular venous oxygen saturation combined witharterial oxygen saturation measurements will indicatecerebral oxygen consumption and so identify ischemicand hyperemic states.

It must always be remembered that the pathologyof head injury is both heterogeneous and dynamic, andthat the dominant cause of raised ICP may vary withtime. Brain injuries do not produce simple or pure

forms of brain swelling.

Indeed one form of brain swelling may inevitablylead to the development of another. For example, anincrease in ICP due to extravascular fluid increase(brain edema) may lead to ischemia and vasodilata-tion, a vascular cause for increased ICP. Conversely,ischemic cytotoxic swelling may later damage the

bloodbrain barrier and cell membranes, leading tovasogenic brain swelling.

Swelling that is predominantly due to increase inblood volume may respond to vasoconstriction andhence to barbiturates or to hyperventilation (Yoshi-hara, Bandoh and Marmarou, 1995). Indeed, the initialeffect of the osmotic diuretic mannitol may also bethrough vasoconstriction induced by lowering bloodviscosity, and therefore dependent on intact vascularreactivity.

Mannitol also increases brain tissue specific gravity,most probably by reducing brain tissue water; hencenon-vascular swelling may also respond to osmotictherapy (Nath and Galbraith, 1986).

19.6 Principles of management

19.6.1 EVIDENCE-BASED GUIDELINES

The many and often conflicting reports and reviewson aspects of head injury pathophysiology and treat-ment have supported a range of different plans ofmanagement (Gahjar et al., 1995; Fearnside et al., 1993).There is now an emphasis on forming guidelines fortreatment based on a rigorous assessment of theavailable evidence. It is inherent to such a process thatthe guidelines be constantly updated in the light ofnew evidence. Guidelines for the Management of Severe

Head Injury was published in 1995 by the BrainTrauma Foundation and the American Association ofNeurological Surgeons and forms an excellent precisof present knowledge.

Because of the clear relationship between ICP andoutcome, most treatment protocols have focused on

avoiding high ICP. Others have argued that theprimary objective of treatment should be to maintainan adequate CPP, i.e. above the lower limit ofautoregulation, as far as it can be judged in the head-injured patient. Rosner suggested that a falling CPPmay set in train a vasodilatory cascade. As CPP falls,vasodilation occurs to maintain CBF. The consequentincrease in CBV raises ICP and further reduces CPP.

Figure 19.4 The relationship between CSF inflow and outflow and viscoelasticity. The viscoelastic properties of brain affectthe equilibrium relationship between CSF pressure and volume (the starting point of the volume pressure curve) and also thedynamic relationship, i.e. the effect of a small volume addition. (Source: reproduced from Miller, 1985, with permission.)


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PRINCIPLES OF MANAGEMENT 391

The cascade is halted by increasing CPP. The con-sequent vasoconstriction will reduce ICP (Rosner andColey, 1986).

Initial reports of the use of CPP-based protocolssuggest improved outcome compared with the TCDB(Rosner, Rosner and Johnston, 1995). However, theprincipal benefit of focusing on CPP may be to reduce

the incidence of hypotension, one of the commonestcauses of secondary insult after head injury (Chesnutet al., 1993a). No particular management protocol hasyet had the benefit of a controlled trial.

It seems clearer now that, although ICP and CPP areinterrelated, both need to be taken into account.

In treating ICP and CPP the following questionsneed to be addressed.

What is the likely cause of increased ICP or reducedCPP?

What levels of ICP and CPP should be maintainedin this patient?

What methods of treatment should be applied and

in what order? What effects might the treatment of ICP or CPP

have on cerebral oxygenation and metabolism?

Since ICP and CPP are indirect indices of brainoxygenation, treatment goals must allow for theanticipated but usually unmeasurable variability inCBF and metabolism resulting from the head injury.For example, pericontusional CBF may be borderlineischemic (18ml/100 g/min), while whole-brain CBF ishigh. CBF is generally reduced in the first 24 hoursafter injury but in the first 46 hours both very lowflows and hyperemic flows (i.e. greater than metabolicrequirements) are found (Salvant and Muizelaar, 1993;Bouma et al., 1991; Chapter 5).

19.6.2 CLINICAL SIGNS OF RAISED ICP

The traditional clinical signs of raised ICP and of amass lesion are in fact quite unreliable (Chapter 8)Furthermore Chesnut et al. (1994) reported that pupil-lary asymmetry was a poor indicator of either thepresence or the side of an intracranial lesion. Theyfound pupil asymmetry of 1mm or more in only 40%of patients with a mass lesion of 25ml or more andonly 33% of patients with pupil inequality of 3mm ormore had an ipsilateral mass lesion. This studyemphasizes the importance of early CT scanning of allpatients with severe head injury.

Nonetheless, it is important to watch for clinicalsigns of brain-stem compression, in so far as this ispossible. Signs of herniation demand treatment what-ever the level of ICP, and indeed may not be reliablyrelated to the level of ICP or to the degree of midlineshift (Marshall, Toole and Bowers, 1983).

19.6.3 WHO IS MONITORED?

Some 80% of patients with severe closed head injury(GCS < 8) will have some degree of raised ICP when

first monitored. In about 40% ICP is greater than20 mmHg at some time after injury, despite therapy(Miller et al., 1979).

CT features will identify most patients who have orare likely to have raised ICP (Chapter 9).

The most important features are:

midline shift; obliteration of CSF cisterns around the brain stem

(Eisenberg et al., 1990; Marshall et al., 1992).

Even in a patient who is able to talk, a midline shift ofgreater than 1.5cm due to an acute traumatic lesionwill invariably predict later deterioration (Marshall,Toole and Bowers, 1983).

Patients with severe head injury and a normal initialCT scan have a 1015% chance of developing raised

ICP later (Eisenberg et al., 1990; Narayan et al., 1982).Risk factors for later onset of high ICP in this group

were:

age over 40 years; BP less than 90 mmHg; unilateral or bilateral motor posturing.

If none or one of these factors was present, theincidence of raised ICP was only 4%, whereas if two ormore were present it rose to 60%.

However, those with a normal initial scan who werenot monitored should have a repeat CT scan at 12 24hours (Narayan et al., 1982).

In another study, seven of eight patients with severehead injury (GCS < 8) whose initial CT scan wasnormal developed intracranial hypertension of morethan 20 mmHg for 5 minutes, and five of thesedeveloped ICP greater than 30mmHg. CPP wasreduced below 60mmHg in five patients (OSullivanet al., 1994).

Hence, in severely head-injured patients with anormal initial CT scan, there is an incidence of raisedICP and critically reduced CPP, which will only beapparent if they undergo close and continuous mon-itoring of ICP and CPP or, if they have low risk factors,close clinical monitoring and repeated CT.

It is our practice for all patients in coma, defined asa GCS of 8 or less after resuscitation, to be ventilatedfor CT scanning. If the CT scan is normal and there areno other adverse features, then sedation will ceasewithin 24 hours and their neurological status isreviewed. Patients who have been transferred fromanother hospital by retrieval team are usually intu-

bated and ventilated for stability during transfer andtheir initial neurological status may be in doubt


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(Chapter 8). A decision about continuing monitoringwill also depend on the CT and, if that is normal, onneurological status after reversal of sedation.

The criteria for ventilation and ICP monitoringare:

GCS 8 after resuscitation with an abnormal scan,

or with a normal scan and at least two adversefeatures i.e. age> 40 years; BP < 90 mmHg afterresuscitation; unilateral or bilateral motorposturing;

GCS 10 and abnormal CT scan; a tight brain at operation following removal of a

clot; ventilation necessary for other injuries, especially

chest injuries.

19.6.4 TREATMENT GOALS

(a) ICP levels

A number of studies have considered the level of ICPthat should be treated.

Patients were found to have a higher morbiditywhen ICP exceeded 20mmHg (Miller et al., 1981) andimproved outcome was reported when ICP wasmaintained below 15 mmHg (Marshall, 1980; Saul andDucker, 1982). Saul and Ducker (1982) suggested thatearly and aggressive treatment of modest rises of ICPmight avoid more significant rises late. Contant et al.(1993) found that critical values independently relatedto outcome were ICP more than 25mmHg, BP lessthan 80mmHg and CPP less than 60 mmHg.

The safe level of ICP in a particular patient maydepend on the accompanying CPP and on thepathology.

Miller (1992) recommended treatment when ICPexceeded 25 mmHg in the first 2 days and 30 mmHgthereafter, providing there were no signs of brainherniation.

As stated earlier, signs of herniation may occur atonly moderately elevated ICP, e.g. less than 20 mmHg,particularly with bifrontal or temporal contusions(Andrews et al., 1988), and these signs demandimmediate treatment whatever the pressure level(Johnston and Jennett, 1973, Marshall et al., 1983). Forthis reason Chesnut, Marshall and Marshall recom-mended always treating ICP greater than 20mmHglasting more than 20 minutes but, with lesions in thetemporal fossa or deep inferior frontal lobes, treatingICP greater than 15mmHg (Chesnut, Marshall andMarshall, 1993).

It is our present practice to aim for ICP below20 mmHg but on occasion to accept higher pressures ifCPP can be held over 70 mmHg and there are no signsof brain-stem herniation.

(b) CPP levels

CPP should be maintained above the expected lowerlimit of autoregulation, that is above the level atwhich CBF will be expected to fall.

In a particular patient, this level will depend upona number of factors.

Pre-existing hypertension. In chronically hyper-tensive patients the upper and lower limits ofautoregulation are raised, so they tolerate hypo-tension poorly; i.e. CBF will begin to fall at ahigher level of CPP than in normotensive patients(Strandgaard and Paulson, 1992). Conversely theywill tolerate higher levels of systemic hyper-tension without increase in CBF.

Susceptibility of injured brain to additionalinjury. Prior injury may reduce brain tolerance tohypotension and hypoxia (Jenkins et al., 1989)

Hence, more severe injuries may be more suscepti-ble to the effects of secondary injury.

Mechanism of reduction of CPP. CBF will beginto fall at a higher level of CPP when CPP isreduced by hemorrhage hypotension rather than byraised ICP or hypotensive medication (Figure19.5).

The pattern of brain injury. CPP is a globalmeasurement and brain injury is typically inho-mogeneous. There may be brain regions where

perfusion is marginal even though global CPP andCBF are adequate. CBF may be reduced aroundcontusions or beneath subdural hematomas (Sal-vant and Muizelaar, 1993), by compression ofvessels due to brain shift or by vasospasm. Inareas of ischemia, tissue acidosis may cause max-

imal vasodilatation so that any fall in globalperfusion will result in a fall in regional bloodflow.

Without direct measurement of CBF, the lowerlimit of autoregulation can be estimated from chan-ges in middle cerebral artery flow velocity measured

by transcutaneous Doppler (TCD). As described inChapter 13, below a CPP of 70mmHg, pulsatilityindex may rise and jugular venous oxygen saturationfall, indicating the onset of hypoperfusion (Chan etal., 1992). Increasing CPP above 70mmHg did notimprove cerebral oxygenation further, suggestingthat a CPP of 70mmHg was adequate.

Hence although ICP and CPP are inter-related,both must be taken into consideration in settingtreatment goals. Brain swelling may progress despitean adequate CPP and in this situation steps must betaken to reduce ICP. However, providing there is nomidline shift or evidence of other brain herniation,and CPP is maintained, moderate increases in ICPcan probably be accepted (Miller, 1992).


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TREATMENT 393

19.7 Treatment

19.7.1 CONTROLLING ICP AND CPP DURING

TRANSFER

(a) From the accident site

Apart from intracranial hemorrhage, the major earlyrisks to the patient with a head injury are hypoxia(P

aO2

< 60 mmHg) and hypotension (BP< 90 mmHg;Fearnside et al., 1993; Chesnut et al., 1993b). Cardio-pulmonary resuscitation is always the first priority, asset out in the ATLS program in Chapter 15. The patientwith a severe closed head injury should be presumed tohave raised ICP and factors that may further increaseICP should be avoided. Urgent attention to airway,

breathing and circulation will reduce cerebral hypoxiaand hypoperfusion (Chapter 15). Normoxia and nor-mocarbia or moderate hypocarbia (PaCO2 = 2832 mmHg) should be achieved as soon as possible. ICPcan be dangerously increased by overperfusion, hyper-tension, hyperpyrexia, inadequate sedation and inap-propriate anesthetic agents. Intubation and endo-

tracheal suction cause sharp although usuallytransitory increases in ICP. In patients with reducedvolume reserve, however, these stimuli may initiate aprolonged rise in ICP.

Pressure waves may be avoided by adequate fluidresuscitation to maintain CPP. Sedation should besufficient to prevent coughing or gagging duringtransport (Chapter 17).

(b) During transfer between hospitals

Patients who have been intubated and ventilated fortransfer are usually moderately hyperventilated(PaCO2 = 2832 mmHg). If lateralizing signs or pupil-lary asymmetry develop, signs that are highly sugges-tive of a mass, then mannitol may be given. At thesame time, the neurosurgeon at the receiving hospitalshould be alerted. However, mannitol should not begiven routinely as it may interfere with volumeresuscitation and furthermore mask the signs of adeveloping mass lesion.

19.7.2 DEFINITIVE TREATMENT

Following the initial assessment, CT scanning andtreatment of immediate causes of raised ICP such asintracranial clots and enlarged ventricles, a decisionmust be made as to whether to institute continuousventilation in order to treat brain swelling. Basicmonitoring consists of ICP, CPP and central venouspressures. In some institutions it will also include

jugular venous oxygen monitoring and continuoustranscranial ultrasonic Doppler examination.

Raised ICP is treated by removing mass lesionsand/or increasing the volume available for expansionof injured tissue. This may be achieved by:

reducing one of the other available intracranial fluidvolumes:

Figure 19.5 The lower limit of autoregulation under different conditions. (Source: reproduced from Miller, 1985, withpermission)


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CSF by ventricular drainage; cerebral blood volume by hyperventilation or

mannitol; brain tissue water content by mannitol;

removing swollen and irreversibly injured brain; increasing cranial volume by decompression.

(a) CSF drainage

A ventricular catheter is the most accurate method ofmeasuring ICP and also permits CSF drainage. Sincereliable, safe and robust pressure-tip catheters that can

be placed easily in the subdural space or within thebrain parenchyma have become available, ventricularcatheters are being used less often. Certainly, whenventricles are compressed or displaced, they may beimpossible to catheterize, even with ultrasound guid-ance. However, outcome was reported to be better inpatients in whom ICP was controlled by ventriculardrainage alone (Gahjar, Hariri and Patterson, 1993).

Ventricular catheterization should be used when-

ever possible and particularly if the ventricles areenlarged. Drainage of even small amounts of CSFproduces an immediate fall in ICP and a rise in CPP.However if systolic BP has been increased by aCushing response, then sudden release of ICP mayprecipitate a fall in BP and CPP. This can be minimized

by i.v. fluid preloading.CSF drainage pressure should be set at about

20cmH2O since continuous drainage at a low pressuremay lead to collapse of the ventricles and loss of thisavenue for ICP control.

(b) Hyperventilation

Hyperventilation will reduce ICP by vasoconstrictioninduced by alkalosis. The fall in ICP parallels the fallin CBV.

The relationship between PaCO2 and ICP is exponen-tial and follows the volumepressure curve. Bymeasuring the change in ICP induced by change inPaCO2, vascular reactivity to CO2 can be calculated. Inone study (Yoshihara, Bandoh and Marmarou, 1995),patients with severe closed head injury (GCS < 8) werestudied within 24 hours of injury. CO2 reactivity tohypocapnia was reduced by 50% compared withhypercapnia, indicating that at this phase after injuryresistance vessels were in a state of persistent vasocon-striction, possibly due to vasospasm or compression.The volume of blood needed to increase ICP wasestimated from the position on the volumepressurecurve, i.e. on the baseline ICP and the compliancemeasured as the pressure volume index (PVI). The PVIis derived from the slope of the semilogarithmictransformation of the exponential pressurevolumecurve and is the theoretical volume necessary to

increase ICP tenfold. At a baseline ICP of 15mmHg,only 2.5 ml of blood were needed to increase ICP to20 mmHg. This was equivalent to a PaCO2 increase ofabout 3 mmHg. When PVI was less than 15 ml, only4 ml of blood were needed to raise ICP by 10mmHg,whereas if the PVI was greater than 15 ml then twicethat amount was necessary. As the brain became

swollen, so the amount of intracranial blood necessaryto increase ICP also fell, as predicted by the exponen-tial volume pressure curve. This study also confirmedthat impaired blood vessel reactivity was associatedwith a worse outcome.

Apart from reducing ICP rapidly, hyperventilationmay have other beneficial effects.

It may correct brain and CSF lactoacidosis which iscommonly present and associated with poor out-come from head injury (DeSalles, Muizelaar andYoung, 1987).

It may restore pressure autoregulation (Paulson,Olesen and Christensen, 1972) and increase global

O2 metabolism (Obrist et al., 1984; Gennarelli et al.,1979).

It may reverse post-traumatic hyperemia, reducethe associated raised ICP and normalize cerebralglucose uptake (Cruz, 1995).

Cerebral resistance vessels are most sensitive to PaCO2around the normal level of 40mmHg. Even in severeinjury where pressure autoregulation is impaired orabsent, cerebral vessels usually retain some respon-siveness to PaCO2, although it may be less than normal(Enevoldsen and Jensen, 1978; Muizelaar et al., 1991;Newell et al., 1996). Hyperventilation is the most rapidmethod of reducing ICP other than ventricular drain-age. Yoshihara, Bandoh and Marmarou (1995) noted a15-second delay between initiating respiratory changeand fall in ICP. The peak effect occurs in about 30minutes.

Since hyperventilation has its maximal vasocon-strictor effect on normal vessels, it has been sug-gested that it may cause a favorable redistribution of

blood from less injured to more injured or ischemicareas where the vessels are already fully dilated andunresponsive to hypocapnia (reverse steal). Anyredistribution, however occurs within the context ofan overall reduction in CBF and indeed it wassuggested some time ago that prolonged hyper-ventilation might be harmful (Jennett et al., 1977).This has been now been supported by a randomizedtrial, which found that prophylactic hyperventilationapplied to a consecutive group of patients withsevere head injury was associated with a worseoutcome. Prophylactic hyperventilation (PaCO225 2 mmHg) was applied for 5 days to patients witha GCS of 8 or less, 14% of whom had an ICP of morethan 20 mmHg on admission. Hyperventilated


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TREATMENT 395

patients with a GCS of 4 and 5 had worse outcomesat 3 and 6 months. The bad outcome did not occurin a similar group treated by hyperventilation andthe base tromethamine (THAM). Ischemic levels ofCBF were not recorded in any group either by xenonCT or by AVDO2 measurements. However, fluctu-ations in ICP were most marked in the hyper-

ventilation-alone group, perhaps because of vesselhypersensitivity to CO2. It was speculated that thesefluctuations and the time spent at ICP greater than20 mmHg were the determining factors in theincreased mortality in hyperventilated patients, butthat the deleterious effects of hyperventilation might

be avoided by using THAM (Muizelaar et al.,1991).

Cruz (1995) recommended profound hyperventila-tion (PaCO2 < 25 mmHg), with continuous monitoringof cerebral oxygen uptake, in patients with raised ICPand diffuse swelling on CT, and found that in mostpatients oxygen and glucose uptake was optimalunder these conditions.

Other clinical studies have, however, reported a fallin global AVDO2 to potentially ischemic levels in somepatients during hyperventilation to PCO2 = 25mmHg(Sheinberg et al., 1992; Lewis, Myburgh and Reilly,1995).

Once hyperventilation is initiated, CSF begins tocompensate for the systemic alkalosis immediately. Ina study of non-injured rabbits, vessel diameters andarterial and CSF pH returned to baseline by 24 hours,despite continued hypocapnia (Muizelaar et al.,1988).

CBF measured within 6 hours after head injury byxenon CT was below the threshold of infarction(CBF 18 ml/100 g/min) in one-third of patients(Bouma et al., 1991) and is generally below normal inmore than 50% of patients. This early ischemia may beworsened by hyperventilation or by a fall in BP.Hyperventilation might also increase the potential forischemia in patients with vasospasm, which is anincreasingly recognized complication of head injury(Cold, 1989; Yoshida and Marmarou, 1991; Turner etal., 1984).

Hence, hyperventilation to PaCO2 less than28 mmHg should be avoided, especially in the firstday after injury, unless all other measures to controlICP have failed. If profound hyperventilation isundertaken, the return to normocarbia needs to beslow because the increase in P

a

CO

2

will now act as avasodilatory stimulus and cause a rise in ICP (Havill,1984). ICP must be monitored carefully during thisphase.

The present view is that PaCO2 levels below28 mmHg are acceptable only as an emergency, forabout 30 minutes, or when all other means of ICPcontrol have failed.

If prolonged hyperventilation is necessary becauseother ICP control measures have failed, then itspotentially harmful effects may be overcome by theuse of THAM. However, the effects of THAM on renalfunction must be monitored carefully.

Marked hyperventilation and vasoconstriction, par-ticularly in young patients, may reduce venous return

and cardiac output (Muizelaar et al., 1991) and it isimportant to ensure that CPP is maintained, partic-ularly if the patient is nursed head-up (section 19.9.1).

In summary, hyperventilation is an effective methodof ICP control. However, it is best reserved as specifictreatment, e.g. following initial resuscitation until CTscanning, and as short-term treatment for acute ICPrises, rather than prophylactically. If profound hyper-ventilation is used (PaCO2 < 28 mmHg), CPP and PjvO2should be monitored carefully and ventilation titratedto keep the PjvO2 above 6065 mmHg, or AVDO2

below 6 ml. However, it is safer to keep the PaCO2 at3035 mmHg, thus avoiding the potential forischemia.

Ventilation parameters

Hyperventilation for rapid control of ICP can beachieved by increasing stroke rate and tidal volume.However high ventilatory rates and tidal volumesmay also reduce systemic arterial pressure and henceCPP. This may also occur with vigorous hand ventila-tion or bagging, often a very effective way of rapidlyreducing ICP. However, this may be dangerous

because PaCO2 is not controlled and may fall to1520 mmHg.

Positive end-expiratory pressure (PEEP) improvesoxygenation without the need for a high inspiredoxygen fraction (FiO2). It has been suggested that thehigher end-expiratory pressure of PEEP might raisevenous pressure and hence ICP. However, studies inpatients have suggested that ICP is not affected, evenwith intrathoracic pressures of up to 40cmH2O sus-tained for up to 18 hours (Frost, 1977; Shapiro andMarshall, 1978; Cooper, Boswell and Choi, 1985).Others have reported that PEEP is associated withincreased ICP in patients with reduced compliance(Apuzzo et al., 1977; Burchiel, Steege and Wyler, 1981).Hence the effects of PEEP are hard to predict and, if itis used, ICP and CPP should be careful monitored. Fora more extensive discussion on ventilation in headinjury, refer to Chapter 17.

(c) Osmotic agents and diuretics

Osmotic agents have been one of the principal meansof treating raised ICP for many years (Weed andMcKibben, 1919), yet their principal modes of actionare still debated


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Mannitol

Mannitol, a six-carbon hexhydric alcohol of the sugarmannose, molecular weight 182, is a powerful osmoticdiuretic and draws fluid into the vascular compart-ment, thereby increasing circulating blood volumeand reducing blood viscosity. It is not metabolized and

the intact bloodbrain barrier is relatively impermea-ble to it, although in high concentrations or afterprolonged use the normal bloodbrain barrier mayopen, allowing it or other large molecules to enter theextracellular space.

It was originally proposed that the principal action ofmannitol was to reverse the bloodbrain osmoticgradient, thereby drawing water from the brainextracellular space. On this premise the aim oftreatment has been to maintain an osmotic gradient of1020 mosmol. This requires repeated doses of man-nitol with consequent problems of progressive dehy-dration, hypotension and prerenal failure. CVP andurine output need to be carefully watched, particularly

if mannitol is combined with the renal loop diureticfrusemide. Serum osmolarity needs to be checked andhypokalemia corrected with potassium supplements.Normovolemia should be maintained (Chapter 17).

Evidence of a cerebral dehydrating action has comefrom clinical studies. MRI studies have suggested thatmannitol reduces tissue water in edematous but not innormal brain (Bell et al., 1987). In a group of patientswith traumatic intracerebral hematomas and contu-sions, mannitol increased the specific gravity of whitematter, probably by reducing brain water content(Nath and Galbraith, 1986). On the other hand, in non-injured cats there was no change in brain watercontent after mannitol and it was suggested thatmannitol acted by reducing CSF volume (Takagi et al.,1983). Also in non-injured cats, pial artery constrictionwas observed and taken to indicate autoregulation tochange in viscosity (Muizelaar et al., 1983).

In patients with severe head injury, when autor-egulation was intact, mannitol reduced ICP by 27.2%without changing CBF. However, when autoregula-tion was defective ICP fell by only 4.7% and CBFincreased. This strongly suggests that vasoconstric-tion, as well as cerebral dehydration, is a major actionof mannitol (Muizelaar, Lutz and Becker, 1984). Inanother study of patients with severe head injury,mannitol consistently reduced ICP and increased CBFand CPP, the greatest increases in CBF after mannitol

being seen in patients with low initial CPP and veryhigh ICP, i.e. those most likely to have impairedautoregulation (Mendelow et al., 1985).

It is probable that the initial rapid reduction in ICPis due to plasma expansion and decreased bloodviscosity which leads to constriction of the cerebralvasculature to maintain constant CBF. This rapid

response is more likely with bolus injection ratherthan infusion. The more prolonged reduction in ICPmay be due to the osmotic effect.

Mannitol may have other possible beneficialactions.

It may reduce red blood cell rigidity, thus allowing

them to penetrate small vessels and areas ofmarginal perfusion more easily (Burke et al., 1981). It may scavenge free radicals, which have been

implicated in ischemic brain damage. It may reduce CSF production (Sahar and Tsipstein,

1978) and a reduction in CSF volume has beenreported experimentally (Tagaki et al., 1983). How-ever, as argued by Nath and Galbraith (1986), this isunlikely to be an important mechanism for reducingraised ICP when CSF has already been displaced.

Treatment based on the dehydration theory aims atproviding a constant osmotic gradient. However,treatment based on the theory of viscosity autoregula-tion employs the opposite strategy i.e. fluid losses

are replaced accurately to maintain normal osmolalityand normovolemia (Rosner, 1993).

Mannitol dose

Mannitol is usually given in a 20% solution in bolusdoses, rather than as a continuous infusion. ICP fallswithin 510 minutes. The maximum effect occurs inabout 60 minutes and the total effect may last 34hours (James et al., 1977).

Bolus administration minimizes hemoconcentrationand prolongs the effects. Boluses of 0.250.5g/kg(given over 1020 min) may be used and repeated

depending on the response. A dose of 0.25g/kg seemsas effective as 1 g/kg in reducing ICP but may not actas long (Marshall et al., 1978). A Foley catheter should

be inserted and fluid losses should be replaced.Central pressures should be carefully watched and thepatient kept euvolemic. Even so, mannitol may

become less effective with repeated doses because:

replacing the diuresis becomes increasingly difficultand hemoconcentration develops; at serum osmo-lality of greater than 320 mosmol/l there is a risk ofuremia and prerenal renal failure (Stuart et al.,1970);

as osmolality rises, the increase in blood viscositycauses a fall in CPP, which will lead to cerebralvasodilatation and hence to a rise in ICP;

mannitol may enter the extracellular space byopening the normal bloodbrain barrier or where itis disrupted, taking fluid with it and cause arebound rise in ICP (Kaufmann and Cardoso,1992). In practice this was seen more often with ureaand is uncommon with mannitol (James et al., 1977).


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TREATMENT 397

However the gradual increase in extracellular fluidosmolality reduces the osmotic gradient and ren-ders mannitol less effective. This change will occurmore slowly if mannitol is given in boluses ratherthan as an infusion.

It is our practice to avoid osmolality above 320mos-

mol/l. Calculated osmolality may be significantly lessthan measured osmolality in the presence of mannitol.

Complications of mannitol

Hyperosmotic prerenal renal failure (Cottrell et al.,1977; Feig and McCurdy, 1977).

Electrolyte disorders. Hypokalemia usually occursafter a few days of treatment and requires potas-sium supplements.

Dehydration and hypotension. Reduced vascularvolume leads to hypotension and the added risk ofcerebral ischemia due to a fall in CPP. This is aparticular risk in those with multiple injuries, the

aged and those with pre-existing cardiac disease.These patients need careful monitoring of centralpressures (Chapter 16).

Expansion of an intracranial hemorrhage. Byshrinking the brain, osmotic diuretics may assist thecontinued expansion of an intracranial clot. Whenthe effects of mannitol wear off, there may be anacute deterioration. This risk is not proven and theacute deterioration under these circumstances maysimply represent the inevitable enlargement of theclot temporarily masked by the effects of themannitol. In a patient who may harbor a clot,mannitol is very effective in allowing time fortransfer, CT scanning and surgical treatment.

Renal diuretics

Frusemide (furosemide) and other renal loop diureticssuch as ethacrynic acid increase plasma osmolarity bydiuresis (Cottrell et al., 1977; Cottrell and Marlin,1981). They may reduce CSF formation directly (Saharand Tsipstein, 1978). In combination with mannitol,frusemide produces a slightly greater reduction in ICPand increases the duration of its effect (Pollay et al.,1983; Wilkinson and Rosenfeld, 1983). Given alone,frusemide and other renal diuretics do not reliablyreduce ICP.

The combination of frusemide and mannitol increa-ses the risk of hypovolemia and renal failure andshould be reserved for patients with actual or incipi-ent cardiac failure or pulmonary edema. When used itis important to avoid excessive dehydration andsodium loss.

Dose: frusemide 2040 mg i.v.; monitoring: serumand urinary electrolytes and fluid balance.

(d) Barbiturates

High doses of barbiturates will frequently lower ICPeven when osmolar therapy and hyperventilationhave failed. Barbiturates and the other hypnotic drugs(such as etomidate and propofol), act by reducingcerebral metabolic rate for oxygen (CMRO2) and

producing a coupled reduction in CBF. The con-sequent reduction in CBV leads to a parallel fall in ICP(Michenfelder, 1974). Some degree of retained vascularreactivity to CO2 (Nordstrom et al., 1988; Messeter etal., 1986) and brain electrical activity must be presentfor barbiturates to act. The maximum effect has beencorrelated with EEG burst suppression, again under-scoring the relationship between reduced metabolicrate and fall in ICP.

Anesthetic equivalent doses of hypnotics are neces-sary and hence ventilation and ICP monitoring aremandatory. Systemic hypotension and pulmonaryfailure may occur. Cardiovascular status, includingcentral venous and pulmonary artery wedge pressures,

must be carefully monitored.If BP falls and cannot be maintained by volume

transfusion then CPP must be maintained by inotropeinfusion. It is safest to set up an inotrope infusion inanticipation whenever barbiturates are given.

Barbiturate therapy is generally reserved for the1215% of patients in whom other forms of intensivemedical therapy for raised ICP have failed. Twouncontrolled trials reported an improved outcomewith barbiturates (Marshall, Smith and Shapiro, 1979;Rea and Rockswold, 1983). In one trial about half thosepatients who failed to respond to other ICP therapyresponded to barbiturates. The mortality in the barbitu-rate responders was 33% compared with 75% in thenon-responders: 69% of survivors were classed as goodrecovery/moderate disability at follow-up (Rea andRockswold, 1983). Similar results were reported in theearlier study (Marshall, Smith and Shapiro, 1979). In acontrolled trial, patients were randomized to barbitu-rate therapy after other medical management for raisedICP had failed. ICP was controlled in about 30% of the

barbiturate group compared to 16% of those treatedwith conventional therapy (Eisenberg et al., 1988).Thus, in each trial, barbiturates were able to control ICPin some patients, even when all other medical meanshad failed and failure to respond to barbiturates carrieda high mortality and morbidity. In contrast to thesestudies, when barbiturates were given prophylac-tically, i.e. to all patients, no benefit was found (Ward etal., 1985; Schwartz et al., 1984).

Thus there appears to be a small subgroup ofpatients with severe head injury in whom barbituratetreatment is beneficial.

At present barbiturates are generally used in thefollowing situations:


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as part of a stepwise protocol for ICP control, onceother medical management has failed (see Figure19.6).

for acute intraoperative brain swelling (Shapiro etal., 1973; Bricolo and Glick, 1981).

It has been suggested that hypnotic therapy, using

barbiturates and other anesthetic drugs, may bespecifically indicated in patients in whom ICP iselevated by vascular or hyperemic brain swelling, asindicated by decreased arteriovenous oxygen differ-ence (SjvO2 > 75%) and preserved electrical activity(Dearden and McDowall, 1985; Miller, Piper andDearden, 1993). Miller et al. have recommended that inthis group of patients, hypnotic therapy should begiven early, since barbiturate and other hypnoticagents will only work if vascular reactivity to arterialCO2 is still present (Nordstrom et al., 1988) and brainelectrical activity is preserved (Bingham et al., 1985).

Hyperemic diffuse brain swelling is found mostoften in young patients, who usually show an ICP

trace in which the amplitude of the arterial pressureoscillation is more than twice that of the respiratoryoscillation (Miller, 1992; Dearden and Miller, 1989;Aldrich et al., 1992). Chesnut, Marshall and Marshall(1993) have also suggested that young patients withmarkedly increased ICP and CT grade 3 or 4 swelling(Chapter 9) may sometimes benefit from early barbitu-rate treatment. However, they emphasized that theevidence for such a specific benefit is anecdotal andearly aggressive barbiturate treatment cannot be gen-erally recommended.

Actions of barbiturates

The actions of barbiturates include:

a decrease in metabolic rate with coupled reductionin CBF;

free radical scavenging and reduction in lipidperoxidation;

a direct increase in vasomotor tone.

Complications and contraindications

Hypotension. This is the main complication ofbarbiturate therapy and is due to reduced systemicvascular resistance and myocardial depression.Existing cardiovascular instability, hypotension andhypovolemia increase the risks of barbiturate ther-apy, lowering the safe dose that can be given andtherefore reducing the likelihood of ICP control.Consequently patients must be euvolemic before

barbiturates are started. Anergy, so that infection may occur without leuko-

cytosis or fever.

Hypothermia. Moderate hypothermia may be bene-ficial. However, below a core temperature of 32C therisk of cardiac complications increases markedly.

Complications of prolonged coma such as decubi-tus ulcers and venous thrombosis.

Gastric stasis. This usually necessitates parenteralfeeding.

Inability to diagnose brain death by clinicalcriteria for 24 hours or more after treatment hasstopped.

Monitoring

Barbiturate coma should only undertaken in anexperienced Intensive Care Unit. Monitoring shouldinclude ICP, BP via an arterial line, CPP, central venousand pulmonary artery catheters and core temperature.

Pupillary responses

Moderate levels of barbiturates cause small pupils

that are sluggish or non-reacting. They may stilldilate in response to brain-stem pressure. Larger dosesmay produce mid-position to 5 mm non-reacting

pupils (Chapter 8), which may produce a stateindistinguishable from brain death (Chesnut, Marsh-all and Marshall, 1993). Widely dilated pupils, partic-ularly if unequal, should always suggest the possibil-ity of a mass lesion. During reduction of barbituratedosage, pupil reactions are the first neurological

function to recover and motor responses are the last(Chesnut and Marshall, 1993).

Endpoints

ICP control: this is the principal endpoint; EEG: EEG burst suppression is a useful guide to

optimal barbiturate dosage; there is no benefit inachieving higher barbiturate levels;

Serum barbiturate levels: most authors advocateserum levels of about 3040 mg/dl for optimal ICPcontrol; however it is doubtful whether routineserum levels are really necessary except to deter-mine when clinical tests of brain function are likelyto be valid.

Dose and duration

Thiopentone. An i.v. bolus of thiopentone (e.g.250 mg) will reduce ICP within seconds, but theeffect will last for only 1520 minutes. This may bea useful test to see whether a patient is likely torespond to prolonged barbiturate therapy. Oncetissue levels have built up after continuous orrepeated doses, the half-life is similar to that of thelonger-acting barbiturates more commonly used.


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TREATMENT 399

Pentobarbitone. Loading dose 10mg/kg over 30min or 5 mg/kg

hourly for 3 hours; Maintenance 1 mg/kg/h or adjusted to serum

level of 3040 mg/dl or to burst suppression(Eisenberg et al., 1988).

Reducing barbiturate therapy

Once ICP control has been achieved for 2436 hoursbarbiturates may be reduced. Despite their long half-life it is preferable to reduce them slowly in order toprevent ICP overshoot.

(e) Other agents

Hypertonic saline

A 15% solution of sodium chloride was the first agentused experimentally to reduce raised ICP. It waspresumed to act by osmosis but the effect was found

to be short-lived and it gained no place in clinicalpractice (Weed and McKibben, 1919). However hyper-tonic saline has more recently been found to be usefulin patients who no longer respond to mannitol and aredeveloping uremia. Intravenous hypertonic saline(30% or 5 mmol/ml) over 10 minutes may produce aprolonged reduction in ICP without diuresis andimprove renal function in dehydrated patients (Worth-ley, Cooper and Jones, 1988). Small amounts ofhypertonic saline may help to prevent hypovolemia inpatients requiring large amounts of mannitol (Ropper,1993). In animal models of focal brain injury andhemorrhagic shock, resuscitation with hypertonicsaline increased CBF at a lower ICP than did Ringer ssolution (Walsh, Zhuang and Shackford, 1991).

Dose: hypertonic saline (5mmol/ml) up to 50 mlover 1015 min; monitoring; serum Na+; urinaryoutput.

Steroids

Because of their effectiveness in treating the brainswelling associated with brain tumors and abscesses,steroids were at one time widely used in traumaticbrain swelling. However, several trials, some usingvery high-dose steroid regimes, have failed to identifya benefit (Saul et al., 1981; Dearden et al., 1986;Gudeman, Miller and Becker, 1979; Cooper et al.,1979).

The was a single exception (Gobiet, 1977). Howeverwhen this study was reanalyzed the changes aftersteroids were found not to be statistically significant(Cooper et al., 1979). Steroids probably have no placein the routine management of closed head injury.However a non-glucosteroid, the 17 amino steroid

(tirilazad), has shown promise in experimental headinjury and is presently undergoing phase 3 clinicaltrials (Hall et al., 1988). The present status of thisand other neuroprotective agents is discussed inChapter 21.

Gamma hydroxybutyrateGamma hydroxybutyrate is an analog of the inhibi-tory neurotransmitter gamma-amino butyrate acid(GABA) and is used as a short-acting anesthetic agent.It is a potent vasoconstrictor and reduces cerebralmetabolic rate. When given as a bolus it has beenshown to be as effective as sodium thiopentone inreducing ICP and with a longer duration of action. Aswith sodium thiopentone it will reduce systemic bloodpressure and CPP must be carefully monitored (Leg-gate, Dearden and Miller, 1986).

Dose: 60mg/kg body weight; monitoring: cerebralperfusion pressure, since it may reduce systemic bloodpressure.

Indomethacin

Indomethacin, a prostaglandin inhibitor, may reduceraised ICP even though other medical treatments,including barbiturate therapy, hyperventilation andmannitol have failed (Jensen et al., 1991; Biestro et al.,1995). Indomethacin may act by restoring the capacityfor autoregulation and hence the response to hyper-ventilation and to mannitol. If indomethacin infusionis withdrawn suddenly there may be a rebound rise inICP (Biestro et al., 1995).Dose: bolus 50 mg in 20 min; infusion 1030 mg/h.

Lidocaine

Lidocaine is a local anesthetic which may be given asan endotracheal aerosol to prevent ICP rises duringintubation (Yano et al., 1986). It may also be givenintravenously for the same purpose (Donegan andBedford, 1980). This may cause myocardial depressantand requires ECG monitoring. Lidocaine has beenused to treat refractory status epilepticus, but highdoses may lower the seizure threshold. There is someevidence that it will lower raised ICP refractory toother methods but it has not been widely used becauseof the potential complications. At the doses usedpreintubation, such complications are unlikely.

Dose: 11.5 mg/kg i.v. within 6090 s of intubation,or as a 4% intratracheal aerosol; monitoring: ECG.

Tromethamine (THAM)

The base tromethamine has been proposed as a meansof correcting the lactic acidosis frequently found in


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patients after head injury (Rosner and Becker, 1984b).In a randomized trial of the effects of prophylactichyperventilation, Muizelaar et al. (1991) found that thepotentially adverse effects of hyperventilation wereprevented and that ICP was more stable. In a furtherprospective, controlled study, the addition of THAMto conventional treatment resulted in better ICP

control. However there was no improvement inoutcome (Wolf et al., 1993). Hence, THAM may beuseful in controlling raised ICP but its place needs to

be more clearly defined in further studies. THAM mayimpair renal function and this needs to be carefullymonitored.

Dose: 1 mg/kg/h of 0.3 mmol/l solution; monitor-ing: renal function.

(f) Hypothermia

Moderate hypothermia (core body temperature3034C) was recommended many years ago in thetreatment of head injury (Sedzimir, 1959) but after

some initial interest it was little used. However,recent experimental evidence suggests that moderatehypothermia is cytoprotective after severe globalischemic insults. Hypothermia reduces the effects of

global ischemia in head injury. It reduces glutamaterelease and prevents the depletion of high-energy

phosphate compounds (Chopp et al., 1991; Busto et al.,1989). A significant improvement in recovery was

found following fluid percussion injury in rats whenhypothermia was initiated up to 15 minutes after theinjury (Clifton et al., 1991). Similarly, cerebral damage

following epidural compression was reduced in acanine model (Pomeranz et al., 1993).

Recent clinical studies have suggested a benefitfrom moderate hypothermia used prophylactically for2448 hours following severe head injury (Marion etal., 1993), or when ICP is not responding to medicaltherapy, including high-dose barbiturates (Shoizaki etal., 1993). In both studies there was a reduction in ICP,CBF and CMRO2 and a trend towards improvedoutcome in the hypothermic groups, more evident in alater report (Marion and Carlier, 1995). There has beenno greater incidence of significant complications withmoderate hypothermia in the head injury studiesreported so far. Hypothermia is well known to causecoagulopathy, but Resnick, Marion and Darby (1994)found no greater incidence of measurable coagulop-athy or of delayed intracerebral hemorrhage in a smallstudy. Metz et al. (1996) found that platelet count fellduring 24 hours of hypothermia and for up to 24hours after rewarming, but there was no significantchange in coagulation tests. Four of ten patientsdeveloped signs of pancreatitis, which reversed withrewarming. Thus hypothermia may be a safe addi-tional treatment in patients with high ICP. Currently, a

large multicenter placebo-controlled trial of prophy-lactic moderate hypothermia (32 2C) is under wayin neurosurgical centers in the USA to test its effectsupon outcome and ICP control.

(g) Hyperbaric oxygen

Hyperbaric oxygen reduces CBF and ICP by vasocon-striction while preserving a high oxygen delivery tothe tissues. Those who respond to hyperbaric oxygenare also likely to respond to hyperventilation, whichhas fewer logistical problems. Hence, even wherepressure chambers are available, hyperbaric oxygen israrely used in the management of patients with headinjury. In one prospective study, hyperbaric oxygenreduced mortality after severe head injury by nearly50%, but did not increase the favorable outcome rateamong survivors (Rockswold et al., 1992).

19.8 Surgical treatment

19.8.1 INDICATIONS (Chapter 20)

When there is clear evidence of neurological deteriora-tion and a CT scan shows an intracranial mass lesion,the need for urgent removal is clear. The results ofsurgery for a mass lesion are directly proportional tothe neurological state at the time of evacuation (Beckeret al., 1977; Mendelow et al., 1983). Unnecessary delayin achieving surgical evacuation and lowering ICPmust be avoided under any circumstances. Rarely, ifdeterioration is rapid and there are clear localizingfeatures, then the CT scanner may be bypassed andthe patient taken directly to surgery (Chesnut et al.,1994).

In comatose patients with hemispheric or diffuseswelling and a small surface clot the need for surgicalremoval may be less clear. However the removal ofeven a small surface clot 35 mm thick, extending overseveral cuts, may improve compliance and make ICPmanagement easier. Moreover, duraplasty and crani-otomy itself may reduce ICP dramatically in thesecircumstances. These potential advantages must be

balanced by the risk of brain herniation, venouscompression and increased swelling, even with dur-aplasty. When the patient is stable, there is onlymoderate brain shift, i.e. 5 mm or less, and ICP is lessthan 20 mmHg it may be reasonable not to treat smallsurface clots by surgery initially. However, suchpatients need careful ICP monitoring and CT scansshould be repeated routinely. In general we believethat it is better to err towards removing too many clotsrather than to tolerate high ICP. Knuckey, Gelbard andEpstein (1989) noted that patients with small extra-dural hematomas were more prone to late deteriora-tion if the hematoma was diagnosed within 6 hours of


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MANAGEMENT OF RAISED ICP AND REDUCED CPP 401

injury than if it was diagnosed later. Deterioration inthe latter group was therefore most often due to otherfactors.

Delayed intracerebral hemorrhage

Delayed intracerebral hemorrhages have been recog-

nized for many years. However, the CT scan hasenabled more precise definition and distinction fromswelling around or enlargement of a previous hemor-rhage (Gentleman and Macpherson, 1989). A delayedintracerebral hemorrhage is defined on CT as a lesionof increased attenuation occurring in a previouslynormal area. They are uncommon, being only 2.6% oftraumatic intracranial hematomas in the series ofGentleman and Macpherson, and developed withinhours to days. Some 80% were detected within 48hours of injury. Less than half needed surgicalevacuation. Their potential occurrence makes repeatCT scan mandatory whenever there is an unexplainedclinical deterioration, failure to improve or a rise inICP, even if the initial scan was normal. It wassuggested many years ago that delayed hemorrhageoccurred in areas of focal injury where vasoparalysis,congestion and increased capillary permeability resul-ted in multiple areas of diapedetic hemorrhage (Evansand Scheinker, 1946). Delayed hemorrhage has beenassociated with clotting abnormalities, in particulardisseminated intravascular coagulation (Kaufman etal., 1980), hypotension and hypoxia (Ninchoji et al.,1984).

19.9 Plan of management of raised ICP

and reduced CPPAlthough the evidence for certain components ofhead injury management is sufficient to providemanagement guidelines, there is no controlled studyof any particular combination of treatments thatwould constitute a recommended protocol or criticalpathway. The treatment plans outlined here arethose of two separate institutions and representsomewhat different approaches to the sameproblem.

It must be recognized that head injury is adynamic process that varies in its pathophysiology

between patients, with time, and in its regional

distribution. The usual practice of using a singleprotocol of management for all patients is not ideal.However at present it is difficult to measure cerebral

blood flow and metabolism directly and treatmenttends to be based on probabilities rather than onspecific information. Furthermore there are still feweffective treatments available for brain swelling andincreased ICP.

In order to tailor the treatments that are availableto the specific and evolving pattern of injury in aparticular patient, continuous bedside monitoring of

brain metabolism and substrate delivery arerequired. Methods of providing this information are

becoming available but until it is possible to dis-tinguish specific causes for raised ICP and reduced

CPP in individual patients, treatment regimes willremain sequential.

Despite these limitations it is important that agenerally consistent plan of approach be adopted. Thegoals of management should be:

to identify the dominant pathology; to target treatment to the cause; to avoid secondary insults.

There are three levels of observation upon whichtreatment is based:

clinical;

continuous multimodality monitoring; imaging.

19.9.1 NURSING POSITION

Patients are usually nursed 30 head up after intra-cranial surgery and head injury in order to reducevenous congestion and brain swelling. In mostpatients ICP is lower in this position.

Rosner and Coley (1986) found that in manypatients, although ICP fell with head elevation, therewas also a significant fall in CPP. A fall in CPP was lesslikely when circulating volume was adequate. How-ever this variable response to positional change

highlights the need for adequate fluid replacementand for CPP monitoring (Chapter 17).

19.9.2 EXTRACRANIAL CAUSES OF RAISED ICP

(Table 19.1)

ICP may be increased by a number of extracranialfactors, including nursing procedures such as endo-tracheal suction and physiotherapy. Before concluding

Table 19.1 Factors that affect intracranial pressure

IncreaseHypercarbiaHypoxia (PaO2 < 50mmHg)EpilepsyHyperthermia

DecreaseHypocapniaHyperoxiaHypothermiaBarbiturates

Venous congestion due to intrathoracic pressure; fluidoverload


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that raised ICP is due to intracranial factors, achecklist should be considered.

Airway and head position. Ensure that there is novenous obstruction.

Arterial blood gases. Ensure that PaCO2 is322mmHg.

Core temperature. A rise of 1C can increasemetabolic rate by 10%, thus increasing ICP byseveral millimeters of mercury. Core body tem-perature must be kept below 38C.

Occult seizures. Anticonvulsants have been recom-mended in all ventilated patients with severe closedhead injury because seizures occurring in heavilysedated and paralyzed patients are difficult todetect without EEG monitoring, yet they can lead tomarked increases in CBF and ICP (Marienne, Robertand Bagnet, 1979)

Sedation level. Consider whether the patient isbecoming more conscious and fighting theventilator.

19.9.3 TREATING RAISED ICP AND REDUCED CPP

Treatment protocols should begin with simple nursingprocedures and proceed stepwise to more complexmethods, depending on the response at each stage.Recent studies from Edinburgh and other centers havehelped to define what constitutes a significant second-ary insult and hence to set treatment goals (Jones et al.,1994). When methods of reliably monitoring cerebraloxygenation and metabolism become available, theseparameters can be taken into account.

Treatment endpoints should take into account thetime since injury and nature of the pathology. Therealso needs to be a balance between treating everychange in ICP or CPP from normal and using up theavailable and limited methods of treatmentprematurely.

Treatment should be on the background of:

cardiopulmonary homeostasis and euvolemia; adequate sedation.

These aspects are covered in Chapters 16, 17 and 18.Table 19.2 indicates the changes in the emphasis of

treatment that have occurred in recent years.

First-tier therapy

If ICP rises the first steps are:

check blood gases to ensure normoxia andnormocarbia;

drain CSF; administer mannitol; institute moderate hypothermia.

Refractory intracranial hypertension

If ICP rises above the desired treatment level and CPPfalls despite first-tier therapy, the second-tier therapiesto be considered are:

induced hypertension; barbiturate therapy; decompressive craniotomy; hypothermia; marked hyperventilation (Guidelines for the Man-

agement of Severe Head Injury, 1995).

Before proceeding to more complex treatments it isalways important to recheck for easily reversiblecauses of raised ICP, as set out in section 19.9.2, and toconsider repeating the CT scan.

Treatment algorithms

The staircase protocol used at the Medical College ofVirginia is shown in Figure 19.6. The indications fordecompressive craniotomy within this protocol aresummarized in Chapter 20. The protocol currentlyused at the Royal Adelaide Hospital (Figure 19.7) is

based on maintaining ICP below 20 mmHg and CPPabove 70 mmHg. However, it also takes into accountSjvO2 and TCD data in distinguishing hyperemia and

Table 19.2 Changing emphasis in management of acutehead injury: SjvO2 = jugular venous oxygen saturation;PEEP = positive end-expiratory pressure; ICP =intracranial pressure (Source: adapted from Myburgh andLewis, 1996.)

Previous strategies Current strategies

Reduce intracranialpressure Maintain cerebral perfusionpressure and reduceintracranial pressure

Elective dehydration Euvolemia

Routine osmotherapy Selective osmotherapy(< 300 mosmol/l)

Routine hyperventilation:(PaCO2 < 30mmHg)

Normocapnia: acutehyperventilation to controlrises in ICP prior toimaging, maintain SjvO2above 55%

Routine barbiturates Limited barbiturates

Routine corticosteroids No corticosteroids

Avoid sedation, use muscle

relaxants

Avoid muscle relaxants,

ensure sedation andanalgesia

Avoid PEEP Use PEEP to maintain PaO2

ICP monitoring intraventricular or subduralfluid-filled catheters

ICP monitoring intraventricular orintraparenchymal solid-state systems


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MANAGEMENT OF RAISED ICP AND REDUCED CPP 403

determining the lower limit of autoregulation in orderto define the optimal level of CPP (Lewis, Reilly andMyburgh, 1996). If jugular bulb oximetry is used, acareful protocol must be observed to minimize falsereadings.

Duration of monitoring

ICP and CPP monitoring should continue until thepatient is stable without treatment and the risk of alater deterioration is low. The period of vulnerabilityto secondary insults may be up to two weeks afterinjury. Studies from Edinburgh found two peaks ofreduced CPP. The first, within 24 hours, was mostoften due to hypotension. The second occurred 56days after injury, usually as a result of increased ICP(Cortbus et al., 1995). Unterberg et al. (1993) reportedthe peak incidence of high ICP to be 13 days afterinjury. Late rises occurred after 310 days, particularlyin patients with multiple contusions, and coincided

with a marked leukocytosis. These reports suggestthat patients with severe head injury and abnormalscans should be monitored for at least 6 days, and thatweaning from the ventilator should occur slowly.

If the ICP is low from the outset or has been lowwithout treatment for 24 hours, and the CT scan doesnot show a mass lesion or diffuse swelling, then it isreasonable to cease sedation. If ICP and CPP remain

satisfactory, then monitoring may be withdrawn. Asnoted earlier, it is important to withdraw barbituratetherapy slowly.

Intractable ICP: who manages the patient?

One of the most important advances in the manage-ment of head injury in recent years has been theformation of integrated multidisciplinary services thatextend from the accident site to the trauma hospitaland indeed beyond to the phase of rehabilitation. Theintensive care specialist has played a key role in allstages of acute care. With the emphasis on intensivecare management for patients, the intensivist needs, inaddition to expertise in cardiorespiratory care, adetailed knowledge of the pathophysiology of headinjury and the effects of drugs knowledge that needsto be shared by the neurosurgeon. The neurosurgicalrole extends beyond removing hematomas. The neu-rosurgeon should be involved in determining treat-

ment protocols, assessing and deciding the treatmentplan for each patient and continuing care after theacute phase. During the acute phase neurosurgeonsand intensivists should work in cooperation in deter-mining treatment steps and in counseling relatives.This is particularly important when the question ofwithdrawing treatment arises, which is discussed inmore detail in Chapter 21.

Figure 19.6 The staircase approach to management of ICP and CPP at the Medical College of Virginia. Treatment isinitiated when ICP> 20 mmHg or CPP< 70 mmHg for more than 10 minutes. Inotropes are used at any time, aiming to keepCPP above 7080 mmHg.


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Figure 19.7 Algorithm for the management of acute head injury based on CPP and ICP and taking into account SjO2 andTCD measurements. ICP = intracranial pressure; CPP = cerebral perfusion pressure; CSF = cerebrospinal fluid; RAP = rightatrial pressure; MAP = mean atrial pressure; SjO2 = jugular venous oxygen saturation; TCD = transcranial Doppler. (Source:reproduced from Myburgh and Lewis, 1996, with permission)


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management icp

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